NOTE ON THE CHURCH OF S. THEKLA (CHAPTER XIII.) ON page 209, note 3, I have said that if the mosque Aivas EfFendi (more correctly Ivaz Effendi), which is situated behind the Tower of Isaac Angelus within the old area of the palace of Blachernae, could be proved to stand on the site of a church, the argument in favour of the identification of the Church of S, Thekla with Toklou Dede" Mesjedi would be weakened. Since this book went to the press, my learned friend Mr. X. A. Siderides has shown me a passage in the historical work of Mustapha EfFendi of Salonica, published in 1865, where the mosque of Ivaz Effendi is described as a church converted into a mosque by a certain Ivaz EfFendi who died in 1586, at the age of ninety. In that case we should have a Christian sanctuary whose position corresponded strictly with the position occupied by the Church of S. Thekla " in the palace of Blachernae," an indication not exactly accurate in regard to Toklou Dede Mesjedi. In view of the late date of Mustapha Effendi's work, and the absence, so far as I can judge, of Byzantine features in the structure of the mosque, it is difficult to decide if the arguments in favour of the identification of the Church of S. Thekla with Toklou Ded6 Mesjedi are entirely overthrown by the statement of Mustapha EfFendi.